The correct answer is Schedule App Service autoscale rules to increase instance count on Mondays at 9 AM and scale down on Tuesdays at 9 AM.

Scheduled autoscaling works best when you have a predictable, recurring traffic pattern like a weekly Monday morning surge. Setting a schedule lets you increase instance count before the spike and reduce it after the peak which provides consistent capacity while controlling cost.

Azure App Service and the Autoscale feature support scheduled actions so you can specify the exact days and times and the desired instance counts or scaling behaviour. This is more reliable and operationally efficient for a known weekly pattern than relying on manual steps or ad hoc metric evaluation during the event.

Configure CPU based autoscale rules that only evaluate metrics during Mondays is not ideal because metric based rules are reactive and may not respond quickly enough at the start of a surge, and limiting metric evaluation to a single day is awkward when a scheduled rule directly expresses the expected pattern.

Keep the application on a single instance to reduce costs during quieter weekdays is incorrect because a single instance will likely be overwhelmed during the surge which can cause degraded performance or outages, and scheduled scaling allows cost control without sacrificing availability.

Manually increase the number of App Service instances every Monday morning to absorb the load is not recommended because manual scaling is error prone and labour intensive, and it cannot guarantee timely or consistent scaling in case of schedule changes or human error.

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